When running apt-get upgrade in automated provisioning scripts (like Chef's knife cloudstack), interactive configuration file prompts break the automation flow. This commonly occurs when:

* The package maintainer provides an updated config file
* Your existing config has local modifications
* The system can't determine which version to keep

For Ubuntu 12.04, these dpkg options provide the most robust solution:

DEBIAN_FRONTEND=noninteractive \\
apt-get -y -o Dpkg::Options::="--force-confdef" \\
-o Dpkg::Options::="--force-confold" upgrade

Key parameters:

• --force-confdef: Uses the default option (keeps old configs when unchanged)
• --force-confold: Preserves local modifications by always keeping old configs

For infrastructure automation, I recommend this complete approach:

#!/bin/bash
export DEBIAN_FRONTEND=noninteractive

# First update package lists
apt-get update -qq

# Then upgrade with conflict resolution
apt-get -y -o Dpkg::Options::="--force-confdef" \\
  -o Dpkg::Options::="--force-confold" \\
  --allow-unauthenticated \\
  --fix-broken install

# Optional: Force upgrade for specific packages
apt-get -y --only-upgrade install nscd bind9

When dealing with config files during upgrades:

For critical systems:

1. Maintain configs in version control
2. Use configuration management tools (Chef/Puppet/Ansible)
3. Test upgrades in staging with --dry-run
4. For NSCD specifically, consider:

# Preserve existing nscd.conf but get new features
apt-get -y install nscd
cp /etc/nscd.conf /etc/nscd.conf.bak
apt-get -y install --reinstall nscd
# Manually merge changes from /etc/nscd.conf.dpkg-new

When running apt-get upgrade in automated deployments (like Chef's knife cloudstack bootstrap), the process halts when encountering modified config files. This creates a chicken-and-egg problem:

# Example of the blocking prompt
Configuration file /etc/nscd.conf'
==> Modified (by you or by a script) since installation.
==> Package distributor has shipped an updated version.
What would you like to do? (Y/I/N/O/D/Z) [default=N] ?

Before solving the automation issue, let's address the second concern about nscd (Name Service Cache Daemon):

• nscd caches user/group/hostname lookups
• Default config usually works for most cases
• If you've customized it, you'll want to merge changes

The definitive solution is to use DEBIAN_FRONTEND=noninteractive:

# In your bootstrap script:
export DEBIAN_FRONTEND=noninteractive
apt-get -y -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" upgrade

This combination:

• --force-confdef: Uses package maintainer's version if unchanged locally
• --force-confold: Keeps old config files when they exist

For more control, create a preseed file:

# /etc/apt/apt.conf.d/local
Dpkg::Options {
   "--force-confdef";
   "--force-confold";
}

To handle nscd.conf specifically in Chef:

# In your recipe:
execute "apt-get upgrade" do
  command "DEBIAN_FRONTEND=noninteractive apt-get -y -o Dpkg::Options::='--force-confdef' -o Dpkg::Options::='--force-confold' upgrade"
  action :run
end

# Then manage nscd separately
template "/etc/nscd.conf" do
  source "nscd.conf.erb"
  owner "root"
  group "root"
  mode "0644"
  notifies :restart, "service[nscd]"
end

After deployment, check config file status:

sudo debconf-show dpkg
sudo grep -r "conffile" /var/lib/dpkg/